The present invention relates to a fuel cell using a proton conductor film or the like, a power supply method using the fuel cell, a function card making use of the fuel cell, a fuel supply mechanism for the fuel cell, and a generator using a proton conductive material or the like and a production method thereof.
Fuel cells are generally configured to generate a power from a generator by supplying a fuel gas to the generator. One example of such fuel cells includes a generator having a proton conductor film held between electrodes, wherein a desired electromotive force is obtained by supplying a fuel gas to the generator. The fuel cell of this type has been greatly expected as an on-vehicle power source used for electric cars or hybrid cars, and further, from the viewpoint of the cell structure capable of realizing easy reduction in weight and size thereof, the fuel cell of this type has been actively studied or developed to be applied not only to the existing application field of dry batteries or rechargeable batteries but also, for example, to the application field of portable equipment.
The mechanism of a fuel cell using a proton conductor film will be briefly described with reference to FIG. 34. A proton conductor film 401 is held between a hydrogen side electrode 402 and an oxygen side electrode 403. Protons (H+) dissociated from hydrogen gas migrate in the proton conductor film 401 along the direction shown by an arrow in the figure from the hydrogen side electrode 402 to the oxygen side electrode 403. A catalyst layer 402a is formed between the hydrogen side electrode 402 and the proton conductor film 401, and a catalyst film 403a is formed between the oxygen side electrode 403 and the proton conductor film 401. In operation of the fuel cell, on the hydrogen side electrode 402 side, hydrogen gas (H2) is supplied as a fuel gas from an inlet 412 and is discharged from an outlet 413. During the time that the hydrogen gas passes through a gas passage 415, the hydrogen gas is converted into protons, which migrate to the oxygen side electrode 403. On the oxygen side electrode 403 side, oxygen (air) supplied from an inlet 416 flows to an outlet 418 through a gas passage 417. The protons, which have reached the oxygen side electrode 403, react with the oxygen flowing in the gas passage 417, to thereby generate a desired electromotive force.
In the above-described fuel cell, if hydrogen is used as fuel, on the hydrogen side electrode as a negative electrode, a reaction (H2⇄2H++2e−) occurs at the contact interface between the catalyst and the polymer electrolyte (proton conductor film). If oxygen is used as an oxidizer, on the oxygen side electrode as a positive electrode, a reaction (½O2+2H++2e−⇄H2O) occurs, to generate water. This means that protons supplied from the hydrogen side electrode 402 migrate to the oxygen side electrode 403 through the proton conductor film 401, to react with oxygen, thereby generating water. Such a fuel cell is advantageous in simplifying the system thereof and reducing the weight thereof because it is not required to provide any humidifier for supplying water.
In the above-described fuel cell using the proton conductor film, the proton conductor film 401 and the hydrogen side electrode 402 and the oxygen side electrode 403 disposed with the proton conductor film 401 held therebetween constitute a generator. A current collector for emergence of an electromotive force is formed for each of the hydrogen side electrode 402 and the oxygen side electrode 403.
One example of a known fuel cell having a structure including current collectors will be described with reference to FIG. 35. FIG. 35 is an exploded view in perspective of a configuration of the known fuel cell. A proton conductor film 431, through which dissociated protons migrate, is held between a hydrogen side electrode 432 and an oxygen side electrode 433. A current collector 434 is brought into close-contact with an outer surface, on the side opposed to the proton conductor film 431, of the hydrogen side electrode 432. Similarly, a current collector 435 is brought into close-contact with an outer surface, on the side opposed to the proton conductor film 431, of the oxygen side electrode 433. In the fuel cell of this type, the outer surfaces of the current collectors 434 and 435 are substantially flattened from the viewpoint of stacking. A plurality of the fuel cells each having such a structure can be easily stacked, and consequently, even if an area of each of the proton conductor films 431 of the plurality of the fuel cells is small, it is possible to obtain a large electromotive force as a whole.
The fuel cell having such a closed structure is advantageous in that it can be easily stacked on another fuel cell having the same structure, to thereby obtain a plurality of the fuel cells; however, for the stack of a plurality of these fuel cells, gases must be supplied not only to the hydrogen side but also to the oxygen side for each fuel cell. In particular, the gas must be forcibly fed to the oxygen side. Concretely, compressed oxygen or compressed air is, generally, forcibly fed by a gas supply means such as a gas cylinder or a pump. For example, in a package type fuel cell system disclosed in Japanese Patent Laid-open No. Hei 9-213359, a gas supply means (denoted by reference numeral 7 in FIG. 2 of this document) is provided inside a gas suction portion. As a result, in this fuel cell system, a space for disposing the gas supply means such as a gas cylinder or a pump must be ensured in addition to a portion functioning as a generator, and further, additional equipment for operating the gas supply means must be provided. This causes a problem in degrading the portability of the fuel cell system.
By the way, portable electronic equipment such as a notebook-size personal computer or a portable terminal is configured such that a PC card such as a card shaped memory card is inserted in a slot formed in a side portion of the equipment. The insertion of the PC card makes it possible to easily enhance the function of the notebook-size personal computer or the like while keeping the portability thereof. On the other hand, a power supply device composed of a fuel cell integrated in a removable package. For example, the fuel cell system mountable on equipment, disclosed in the above-described document, Japanese Patent Laid-open No. Hei 9-213359, is of a type using a solid polymer film, wherein the fuel cell system is housed in a cell housing portion of equipment requiring a cell source, for example, a personal computer. With this configuration, a plurality of fuel cells can be stacked in the package, and therefore, even if an area of each of proton conductor films of the fuel cells is small, it is possible to obtain a large electromotive force as a whole.
The fuel cell having such a package structure is advantageous in that it can be easily stacked on another fuel cell having the same structure, to thereby obtain a plurality of the fuel cells; however, for the stack of a plurality of these fuel cells, as described above, gases must be supplied not only to the hydrogen side but also to the oxygen side for each fuel cell. Concretely, compressed oxygen or compressed air is, generally, forcibly fed by a gas supply means such as a gas cylinder or a pump. For example, in the package type fuel cell system described in the above document, the gas supply means 7 in FIG. 2 of this document is provided inside a gas suction portion. As a result, a space for disposing the gas supply means such as a gas cylinder or a pump must be ensured in addition to a portion functioning as a generator, and further, additional equipment for operating the gas supply means must be provided. This causes a problem in degrading the portability of the fuel cell system. Since a function card is generally required to be sized so as to satisfy a size standardized under a JEIDA/PCMCIA standard, it is practically difficult to mount the above-described gas supply means, additional equipment, and the like in a space defined by a standardized thickness of 3.3 mm or 5.0 mm.
To enhance the output (current value) of the fuel cell including the generator composed of the proton conductor film 401, and the hydrogen side electrode 402 and the oxygen side electrode 403 disposed with the proton conductor film 401 held therebetween, it is effective to increase the size of the generator. For example, if the area of the proton conductor film 401 becomes twice, the current value as the output of the fuel cell becomes correspondingly twice.
In the case of increasing the size of the generator composed of the proton conductor film 401, and the hydrogen side electrode 402 and the oxygen side electrode 403 disposed with the proton conductor film 401 held therebetween, however, it is easier to cause irregularities such as camber or waviness on the planar generator. This makes it difficult to ensure uniform contact between the generator and the current collectors. As a result, for the large-sized fuel cell, there occurs a problem that a collection efficiency, that is, a ratio of a power emerged from the generator via the current collectors to a power actually generated in the generator becomes degraded. To realize uniform contact between the generator and the current collectors, it is required to apply an excess pressing force from the current collector side to the generator and to control a distribution of the pressing force. In actual, to realize ideally uniform contact, the structure of the fuel cell may be significantly complicated, and to realize such a structure, the weight and the size must be increased. In some case, such a large, heavy complicated structure obtained for realizing ideally uniform contact may become undesirable as the cell structure.
A known structure for holding a proton conductor film between a hydrogen side electrode and an oxygen side electrode will be briefly described with reference to FIG. 36. As shown in this figure, a proton conductor film 421 is somewhat larger than each of a hydrogen side electrode 422 and an oxygen side electrode 423. In a state that the proton conductor film 421 is put between the hydrogen side electrode 422 and the oxygen side electrode 423, a seal material 424 made from silicon rubber is mounted to the periphery of the hydrogen side electrode 422 and another seal material 424 is mounted to the periphery of the oxygen side electrodes 423 in such a manner as to hold the proton conductor film 421 therebetween. The seal materials 424, which are mounted to surround the peripheries of the hydrogen side electrode 422 and the oxygen side electrode 423, hold the proton conductor film 421 therebetween, and therefore, it can prevent leakage of gases such as hydrogen gas and oxygen gas or air. The hydrogen side electrode 422 is held between the seal material 424 and a current collector 425 having a plurality of holes 426 through which hydrogen is supplied to the hydrogen side electrode 422. Similarly, the oxygen side electrode 423 is held between the seal material 424 and a current collector 425 having a plurality of holes 426 through which oxygen is supplied to the oxygen side electrode 423.
In the fuel cell having such a structure, the pair of elastic seal materials 424 are mounted to both the hydrogen side and the oxygen side in such a manner as to hold the proton conductor film 421 therebetween, and accordingly, if the shape and the material of each seal material 422 are equalized, it is possible to keep a desired gas-tightness because the proton conductor film 421 is held between the uniform elastic bodies. On the contrary, if a thickness error or a variation in elastic characteristic occurs at part of the seal material 424 made from silicon rubber, a deviated stress is applied to the proton conductor film 421, thereby making it difficult to keep a desired gas-tightness around the proton conductor film 421. In particular, when both the seal materials 424 mounted to the hydrogen side electrode 422 and the oxygen side electrode 423 cause shape errors, the possibility of occurrence of leakage of gases at the proton conductor film 421 held by the defective seal materials 424 becomes higher.